This invention relates generally to semiconductor processing utilizing a plasma, and specifically relates to the improvement of plasma distribution and process performance within a plasma generated and sustained through inductive coupling.
Gas plasma generation is widely used in a variety of integrated circuit (IC) fabrication processes, including plasma etching, plasma enhanced chemical vapor deposition (PECVD), and plasma sputter deposition applications. Generally, plasmas are produced within a process chamber by introducing a low-pressure process gas into the chamber and then directing electrical energy into the chamber for creating an electrical field therein. The electrical field creates an electron flow within the chamber which ionizes individual gas atoms and molecules by transferring kinetic energy through individual electron-gas molecule collisions. The electrons are accelerated within the electric field, producing efficient ionization. The ionized particles of the gas and free electrons collectively form what is referred to as a gas plasma or discharge. The plasma may exist at various ionization levels from 10xe2x88x926 up to fully ionized plasma (based on the fraction of ionized particles with respect to the total number of particles).
The plasma particles will generally be positively charged, and are commonly utilized for etching a surface of a substrate within the chamber or depositing a layer of material onto such a substrate. Within an etching process, the substrate may be negatively biased such that the positive plasma particles are attracted to the substrate surface to bombard the surface and thus remove surface particles or etch the substrate. In a sputter deposition process, a target may be positioned within the chamber opposite the substrate. The target is then biased so that plasma particles bombard the target and dislodge, or xe2x80x9csputter,xe2x80x9d target particles therefrom. The sputtered target particles then deposit upon the substrate to form a material layer on an exposed surface thereof. In ionized sputter deposition, hereinafter referred to as iPVD, the sputtered particles are themselves ionized before they are deposited. In a plasma enhanced CVD process, the electrically neutral, active radicals form a deposited layer on exposed surfaces. Generally, there are various different ways of producing a plasma within a process chamber. For example, a pair of opposing electrodes might be oriented within the chamber to capacitatively couple energy to the plasma. A microwave resonant chamber utilizing ultra-high frequency microwave fields might also be utilized. Electron cyclotron resonance (ECR) devices, on the other hand, use controlled magnetic fields in conjunction with microwave energy to induce circular electron flow within a process gas to create and sustain a plasma. Inductive coupling processes are also popular, and are particularly desirable for their capability of producing high-density plasmas. Inductively coupled plasmas (ICPS) generally utilize an inductive element such as a shaped coil or antenna positioned with respect to the processing chamber to inductively couple energy into the processing chamber and thus create and sustain a plasma therein.
For example, in one particular design for an inductively coupled plasma (ICP) system, an inductive coil or antenna is positioned proximate the top portion of the chamber to create a plasma within the chamber. More specifically, the antenna is positioned on one side of a dielectric plate or window at the top of the processing chamber, and electromagnetic energy from the antenna is coupled through the dielectric window and into the plasma. One such design is illustrated in U.S. Pat. No. 5,556,521 which is commonly owned with the present application.
In an alternative ICP processing system, a helical or solenoidal-shaped coil is wound around the outside of a sidewall portion of the processing chamber to inductively couple energy to the plasma through the chamber sidewall, rather than through the top of the chamber. In such a system, a portion of the chamber sidewall is fabricated from a dielectric material through which the inductively coupled energy may pass. One suitable dielectric material for a window or chamber sidewall is quartz. Various ICP systems are known and utilized in the art, as evidenced by various issued patents directed to particular ICP details, such as plasma uniformity, RF matching, and the performance characteristics of the antennas or other inductive elements.
The geometry of an ICP system is a significant factor in determining both the plasma density and uniformity, and ultimately, the processing uniformity over the area of the substrate. For current processes, it is desirable to produce a uniform, high-density plasma, over a significantly large area so that large substrate sizes might be accommodated. For example, manufacturing of today""s ultra large-scale integrated (ULSI) circuits requires a dense, uniform plasma over large substrates having diameters of approximately 200 mm or greater.
More specifically, in an ICP system, the plasma is excited by heating or exciting electrons in the plasma region of the processing chamber. The inductive currents which heat the plasma electrons are derived from oscillating magnetic fields which are produced proximate the inside of the dielectric window or sidewall by RF currents within the inductive antenna or coil. The spatial distribution of those magnetic fields is a function of the sum of the individual magnetic fields produced by each portion or segment of the antenna or coil conductor. Therefore, the geometry of the inductive antenna or coil significantly determines the spatial distribution of the plasma, and particularly the spatial distribution and uniformity of the plasma ion density within the process chamber. As one example, an antenna having an xe2x80x98Sxe2x80x99 shape, such as that disclosed in U.S. Pat. No. 5,669,975, establishes a significant ion density in the central area of the antenna. At higher RF power levels, the outer portions of the antenna will also contribute significantly to plasma ionization. While a significant advantage of an ICP system utilizing such an antenna is the linearity of the system with respect to the power delivered to the antenna and also the radius of the process chamber, and while the current ICP systems and antenna designs utilized therein have provided sufficient plasma generation, such systems still have certain drawbacks.
For example, within the confines of existing ICP systems and antenna configurations, it is difficult to scale the process chamber to a larger size for handling larger substrates without significantly increasing the dimensions of the antenna or coil. An ICP antenna with a larger footprint must be accommodated with expensive modification to the processing system. Furthermore, larger antennas and their associated plasmas exhibit greater sensitivity to process parameters within the chamber. For example, the plasma process, such as an etch or deposition process, becomes more sensitive to process parameters such as the substrate-to-target distance within a sputtering system, the target material within a sputtering system, the pressure within the process chamber, and the height and width configuration of the chamber.
Furthermore, current ICP systems utilizing planar spiral antennas have exhibited asymmetry wherein the distribution of the plasma is not aligned with the central axis of the chamber. Such plasma asymmetry degrades the uniformity of the plasma and the uniformity of the deposition or etch process, thereby affecting the overall system efficiency. Still further, planar antennas may exhibit a ring or doughnut-shaped plasma for one process and corresponding set of parameters, while creating a centrally peaked plasma for another process and other parameters. Accordingly, the plasma shape and uniformity is not consistent within such ICP systems and will be process dependent. Therefore, the overall IC fabrication process will not be consistent from one plasma process to another plasma process.
Another drawback with planar antenna systems utilizing an S-shaped antenna or coil, is that the outer portions of the coil marginally affect the plasmas created by the central region of the coil, thus giving an azimuthal dependence within the plasma, and a corresponding azimuthal dependence in the etched or deposited films on the substrate. That is, along one axis of the plane defined by the coil, the plasma will have a different uniformity and density than along another planar axis of the coil.
Another concern with inductively coupled plasmas is to ensure that energy is predominantly inductively coupled into a plasma rather than predominantly capacitively coupled. Capacitive coupling between the inductive element and the plasma is undesirable. While Faraday shields may be used to reduce capacitive coupling, it is still desirable to improve on the design of such shields within a processing system.
Accordingly, it is an objective of the present invention to overcome drawbacks in the prior art and provide a plasma processing system, and particularly an ICP system, in which a dense, uniform plasma is created.
It is another objective of the present invention to provide a uniform plasma which is less dependent upon the size and shape of the process chamber than current plasma processing systems.
It is still another objective to provide a plasma which is symmetrical in the processing chamber.
It is another objective to reduce capacitive coupling within an ICP system.
It is another objective of the present invention to provide a uniform, dense plasma over a large area, such as an area sufficient to handle a 200 mm or greater wafer, while maintaining a compact and inexpensive design of the inductive coil or antenna.
It is still another objective of the present invention to provide consistent plasma generation and thereby provide consistent processes, such as etch processes and deposition processes, which are less dependent upon process parameters, such as pressure and/or chamber geometry or size.
One attempt to address various of the above objectives utilizes a processing system incorporating unique inductive elements therein. Specifically, U.S. patent application Ser. No. 09/277,526, entitled Process, Apparatus and Method for Improving Plasma Distribution and Performance in an Inductively Coupled Plasma, and filed on Mar. 26, 1999, now U.S. Pat. No. 6,237,526, illustrates such systems. That patent is incorporated herein by reference in its entirety. While the processing systems and inductive elements disclosed therein provide for the creation and use of effective inductively coupled plasmas, it is still desirable to improve and further refine such systems for improved ICP characteristics. As such, the present invention addresses the above objectives and other objectives and is set forth in greater detail below.
A processing system for processing a substrate with an ionized plasma comprises a processing chamber defining a processing space with a substrate support therein for supporting a substrate in the processing space. A gas inlet introduces process gas into the space and a plasma source is operable for creating an ionized plasma therein. In accordance with one aspect of the present invention, the plasma source comprises an inductive element operable for coupling electrical energy into the processing space to create an ionized plasma therein. The inductive element winds around a portion of the processing space inside the processing chamber such that the inductive element is internally contained. In that way, the inductive element is exposed directly to the plasma in the processing space, rather than having to couple electromagnetic energy through a portion of the processing chamber.
In accordance with one embodiment of the present invention, the inductive element is encased inside a dielectric material to physically separate the element from the processing space while allowing the element to couple electrical energy into the processing space. In one example, a dielectric material assembly includes an inner subassembly, an outer subassembly, and a middle subassembly. The inductive element is configured around the middle subassembly, wherein the outer subassembly isolates the inductive element from the grounded processing chamber, while the inner subassembly isolates the inductive element from the processing space and plasma.
The present invention may be suitably used with a number of different inductive element shapes. One suitable shape comprises a coil with multiple coil turns wherein the turns include segments oriented along a chamber sidewall portion and segments oriented along a chamber end wall portion for coupling energy simultaneously into the processing space through both the sidewall and end wall portions of the chamber.
In another embodiment of the invention, a dielectric envelope is positioned within the processing space and surrounds a portion of the inductive element. The envelope encases the element against the processing chamber and isolates the element from the processing space. A dielectric epoxy or other suitable insulating material fills the inside of the envelope for further encasing the inductive element.
In accordance with another embodiment of the present invention directed to an inductive element positioned internally in the chamber, a DC electrical energy source is electrically coupled to the inductive element at a point along the inductive element, and a ground reference is electrically coupled to the inductive element at another point along the inductive element. The DC source is operable for enhancing the magnetization of the inductive element to reduce the capacitative coupling of energy between the inductive element and the plasma, thereby protecting the inductive element exposed to the plasma and the processing space of the chamber. Inductors are electrically coupled between the inductive element and the DC source and ground to further enhance the magnetization of the inductive element.
In accordance with another aspect of the present invention, an electrostatic shield is utilized with the plasma source to enhance inductive coupling of energy into the processing space. The electrostatic shield comprises a body having opposing face surfaces wherein at least one bore is formed in the shield along the body and between the face surfaces. A slot is formed in each of the face surfaces proximate the bore and communicating with the bore to form a passage through the shield. The shield enhances inductive coupling and the unique slots prevent a line-of-sight pathway therethrough to effectively trap particles that might otherwise penetrate the shield and generally prevent transmission of plasma particles through the shield.